Bamboo Shoot Preservation and Storage Techniques: How to Extend Shelf Life Without Spoilage

Bamboo shoots are the young shoots of bamboo, also known as bamboo sprouts. Bamboo is a perennial evergreen herbaceous plant, and the edible portion consists of the newly emerged, tender, plump, short and sturdy shoots or rhizomes. Bamboo originated in China, has many types, strong adaptability and an extremely wide distribution. Worldwide there are 30 genera and 550 species, growing abundantly in tropical, subtropical and temperate regions. China is one of the countries with the most bamboo in the world, with 22 genera and more than 200 species distributed throughout the country, most abundant in the Pearl River basin and the Yangtze River basin; north of the Qinling Mountains, where rainfall is low and temperatures are cold, only a few dwarf bamboo species grow.  Growth habits of bamboo shoots The underground stems of scattered-type bamboo species such as moso bamboo and early bamboo penetrate relatively deep into the soil, and the bamboo rhizomes and shoot buds are protected by the soil layer, so they are not easily damaged by freezing in winter, and the shooting period is mainly in spring. The underground stems of clumping-type bamboo species such as ma bamboo and green bamboo are shallow in the soil, and the shoot buds are often exposed above the soil surface, making them vulnerable to freezing damage in winter, with the shooting period mainly in summer and autumn. Bamboo originated in the tropics and subtropics, prefers warmth and fears cold, and is mainly distributed in areas with annual rainfall of 1000-2000mm. The optimum temperature for moso bamboo growth is an annual average of 16-17°C, with summer averages below 30°C and winter averages around 4°C. Ma bamboo and green bamboo require an annual average temperature of 18-20°C, with the January average temperature above 10°C. Therefore, bamboo forests are lush in southern China, while they are sparse north of the Qinling Mountains-Huaihe River line. Bamboo requires deep soil that is loose, fertile, moist, and well drained and aerated, with a soil pH of 4. 5-7 being suitable.

Bamboo shoots are delicious, often eaten as a vegetable, and also have certain medicinal value. Bamboo shoots are sweet in taste, slightly cold in nature and non-toxic, and have effects such as quenching thirst, promoting urination, clearing the lungs and resolving phlegm. The cellulose contained in bamboo shoots can promote intestinal wall peristalsis, enhance the secretion of digestive glands, facilitate digestion and excretion, and reduce harmful substances stagnating in the intestines, thereby helping to prevent colon cancer. Therefore, bamboo shoots, with their rich nutrition, have become a traditional food loved in people's daily lives.

Bamboo shoots easily undergo lignification at room temperature, which greatly affects their nutrition and quality. After harvesting, if stored at room temperature for 24 hours, 60% of the shoot becomes lignified; after 48 hours, it has almost lost its edible value. Because bamboo shoots are mostly produced in mountainous or hilly areas with inconvenient transportation, it often takes a period of time from harvesting to the sales area, which further aggravates the lignification of green bamboo shoots. China produces 2.1 million tons of bamboo shoots annually, ranking first in the world, and the output is on the rise; according to relevant forecasts, by 2010 China's bamboo shoot output will reach 3-3.2 million tons. Therefore, research on how to preserve green bamboo shoots is of great significance. Commonly used preservation techniques in China include:

(1) Coating treatment. Coating treatment involves removing the outer shell, bottom and roots of the bamboo shoots, then applying a layer of film to the surface of the shoots to slow their respiration rate, thereby slowing the loss of nutrients within the shoots. The main coatings include chitosan coating and konjac glucomannan coating. The general process flow for coating is:

Bamboo shoots→washing→removing roots and bottom shoot shells→color protection (8 minutes)→de-greening→coating→air drying→plastic packaging→weighing→storage.

For coating, chitosan coating is about 1.5%, and konjac glucomannan coating is about 0.2%. The specific concentration should be based on the composition of the coating liquid and the coating process.

In the coating treatment above, the de-greening process is involved, whose main purpose may be to inactivate enzymes at the bottom of the bamboo shoots and kill microorganisms. Generally, the higher the de-greening temperature and the longer the time, the more thoroughly the enzymes are inactivated and microorganisms inhibited. However, after high-temperature, long-duration enzyme inactivation, some bamboo shoots become steamed and soften during storage, causing loss of bamboo shoot juice and actually shortening the storage time. Therefore, the de-greening temperature and time will vary with different bamboo shoot varieties. According to reports, the temperature used during de-greening is about 60°C, for 30-60 seconds.

(2) Chemical reagent preservation. There are mainly two types of chemical reagent preservation: (i) Adding chemical reagents that can release sulfur dioxide and carbon dioxide. The released carbon dioxide increases the concentration of carbon dioxide within the packaging system, thereby inhibiting the respiration rate of the bamboo shoots; sulfur dioxide is used to inhibit microorganisms and enzymes, thereby achieving preservation, and commonly used sulfur reagents include sodium sulfite, sodium metabisulfite, sodium dithionite, etc. (ii) Preservatives. Mainly sodium benzoate, potassium sorbate, sodium chloride, etc. For example, Xu Ping of the Simao region of Yunnan Province used sodium benzoate and sodium metabisulfite as chemical additives for bamboo shoot preservation and succeeded (obtained national patent 90109091). However, because people's requirements for food are gradually increasing, the use of preservatives is subject to certain controls. Therefore, when using preservatives, be sure to pay attention to the scope of use and maximum usage amount of different preservatives.

(3) Low-temperature cold storage. Place the treated bamboo shoots in breathable plastic baskets and place them in a cold storage room, with the temperature generally controlled at 3-6°C and humidity at 85-95%. Proper cooling can effectively reduce the respiration rate within the bamboo shoots and delay the appearance of the respiration peak, greatly delaying the decomposition of proteins, fats, starch and other substances within the shoots.

(4) Film packaging. Put shoot chunks into plastic bags and then seal and store them; vacuum-sealed packaging is also used, and the commonly used plastic bags are mainly PE bags. However, this treatment easily leads to anaerobic respiration in bamboo shoots, thereby worsening their quality. Therefore, this method is often combined with other methods, such as low-temperature storage, adding solid slow-release agents that can release sulfur dioxide and carbon dioxide into the packaging bags, activated carbon, etc.

Bamboo shoot storage:

Optimum storage temperature: 0°C

Relative humidity: above 95%RH

The tenderness of bamboo shoot tissue is an important factor determining its commercial value. Just after being cut from the plant, the tissue metabolic rate is extremely high, and fiber formation is quite rapid. Therefore, rapidly pre-cooling after harvest to lower the product temperature is a key to maintaining good quality in bamboo shoots. Use water cooling to lower the shoot temperature, preferably to below 5°C. For storage and transport within one day, it must at least be lowered to below 15°C, which can significantly delay fiber formation. If the storage period is to be extended after transport, it is best to store at below 5°C, close to 0°C, keeping the relative humidity of the environment at 95-100%RH. After harvesting bamboo shoots, if the storage and transport temperature is high, never seal them in plastic bags, otherwise off-flavors will be produced due to anaerobic respiration, reducing quality.

Storage temperature (°C) 0 5 10 15 Room temperature (25°C)

Storage period (days) 20-30 14-20 3 1 Within 1 day